1. Field of the Invention
The invention relates generally to an integrated lead suspension (ILS) for connection of read/write circuitry to the read/write head in a magnetic recording hard disk drive (HDD), and more particularly to an ILS with optimal characteristic impedance.
2. Description of the Related Art
In magnetic recording HDDs, the read/write head is formed on an air-bearing slider that rides on a thin film of air above the rotating disk. A mechanical suspension comprised of a flexure with a gimbal at its end connects the slider to the disk drive's actuator arm. The slider is attached to the gimbal which allows for slight movement on the air bearing as the disk rotates.
Electrical connection is required from the read/write circuitry, typically a read pre-amplifier/write driver module or chip, through a flex cable and suspension to the read and write elements on the slider. A suspension that integrates the mechanical connection with the electrical connection is called an integrated lead suspension (ILS) that is connected between the flex cable and the gimbal. A typical ILS is a generally flexible laminate of a conductive metal substrate like stainless steel, an insulating dielectric layer like polyimide, and electrically conductive copper lines or traces patterned on the dielectric layer.
The write driver circuitry typically provides a single-point input to the ILS for each of the positive and negative write signals (+W and −W). The write driver circuitry provides current through the ILS and then to the write element or head. The write driver circuitry power supply voltage and performance of the current through the write head depends on the characteristic impedance of the ILS. The write driver circuitry is required to supply signals with a wide frequency band, which requires optimizing the characteristic impedance of the ILS. However, there are physical constraints in the design of the ILS that become challenges to achieve the optimal characteristic impedance. For example, the flex cable and gimbal may both have fixed impedances of unfavorable values and the ILS may have a fixed length, which present difficulties in optimizing the characteristic impedance of the ILS. Moreover, capacitive loading at pads and vias along the ILS may also add non-negligible lumped disturbances to the wideband signals transmitted from the write driver circuitry to the write head.
What is needed is a HDD with an ILS with optimal characteristic impedance and a method for designing the ILS to have optimal characteristic impedance for wideband signal integrity under various physical constraints.